Tenocytes from ruptured and tendinopathic Achilles tendons produce greaterquantities of type III collagen than tenocytes from normal Achilles tendons - An in vitro model of human tendon heating

Type I collagen is the main collagen in tendons; type III collagen is prese nt in small amounts. Ruptured Achilles tendons contain a significantly grea ter proportion of type III collagen, which predisposes them to rupture. We used an in vitro model to determine whether tenocytes from Achilles tendons that were ruptured (N = 22), nonruptured (N = 7), tendinopathic (N = 12), and fetal (N = 8) show different behavior. Samples of Achilles tendon were digested with collagenase and the released tenocytes were collected. Primar y tenocyte cultures were established and subsequently cultured onto glass c overslips. Once a confluent monolayer was obtained, the cell populations we re "wounded" by scraping a pipette tip along the surface. The cultures were further incubated for either 1, 4, 8, 12, 16, or 24 hours, and production of types I and II collagen was assessed by immunostaining. In cultures from ruptured and tendinopathic tendons, there was increased production of type III collagen. Athletic participation places excess stress on the Achilles tendon, which could potentially lead to areas of microtrauma within the ten don. These areas may heal by the production of type III collagen, which is an abnormal healing response. Accumulation of such episodes of microtrauma could re-suit in a critical point where the resistance of the tissue to ten sile forces is compromised and tendon rupture occurs.